The present invention relates to a piston for an internal combustion engine.
Japanese Patent Application Unexamined Publication. No. 2009-221900 A recites a piston for an internal combustion engine which includes a cylindrical skirt portion, a crown portion integrally formed on an upper end of the skirt portion, and generally cylindrical pin boss portions integrally formed with the skirt portion so as to be opposed to an inner peripheral surface of the skirt portion, the in boss portions having pin insertion holes through which a piston pin extends and supporting both end portions of the piston pin. The crown portion has a thickened wall portion formed on an outer peripheral side of the crown portion along a circumferential direction thereof. The thickened wall portion has a generally ring-shaped cooling channel therein which is a cooling passage for allowing such a cooling medium as a lubricating oil to flow through and cool the crown portion. Further, an introduction hole and a drain hole are formed at a lower end of the thickened wall portion and opened into the cooling channel.
Introduced from the introduction hole into the cooling channel is a lubricating oil injected from an oil jet disposed on a cylinder block in the vicinity of a bottom dead center position of the piston. The lubricating oil flows through the cooling channel, and then is discharged from the drain hole. By thus flowing the lubricating oil in the cooling channel, heat in the piston is absorbed by the lubricating oil so that the piston can be cooled.
Further, when changeover of acceleration of the piston in an up-and-down direction occurs in accordance with up-and-down movement of the piston, the lubricating oil in the cooling channel causes interference along an inner peripheral surface of the cooling channel to splash on the inner peripheral surface of the cooling channel. As a result, the lubricating oil is contacted with the whole inner peripheral surface of the cooling channel, thereby enhancing an efficiency of absorption of heat in the piston.